1. Field of the Invention
The invention relates to an electrophotographic photosensitive member used in electrophotographic imaging processes, and more particularly to a electrophotographic photoreceptor for xerographic systems.
2. Description of the Prior Art
Recently, an amorphous silicon nitride containing H, amorphous silicon carbide containing H or amorphous silicon oxide containing H, each hereinafter referred to as a-SiN, a-SiC or a-SiO photoconductive film, respectively, have been utilized for a photoconductive layer of an electrophotographic photoreceptor; namely, because photoreceptor composed of such photosensitive members show (1) long life, (2) are to men and (3) have photosensitivity.
a-SiN, a-SiC or a-SiO photoconductive film has been prepared by plasma CVD and sputtering methods, where H content in these films has been limited to be in the range of 10-40 atomic % (see U.S. Pat. No. 4,471,042).
Each of the a-SiN, a-SiC and a-SiO photoconductive films can achieve, only by prescribing the specific amount of N, C or O in the film and by with B, reach dark conductivity of about 10.sup.-13 .OMEGA..sup.-1 cm.sup.-1 to be usable a photosensitive member. While a-SiC and a-SiO photoconductive films have a lower dark conductivity, they simultaneously have lower photosensitivity, so that practical use has been hindered in this regard. Also, it has been demonstrated in the inventor's experiments that in repeated operation on next charging process after exposure or photo-discharge, the surface potential of a-Sin photoconductive film lowers 20% or more from an initial value. In other words, the conventional type photoreceptor using a-SiN film as a photoconcuctive layer is quite poor in dark decay characterisics to thereby not be suitable for practical use. This may be due to the fact that gap states such as dangling bond density of Si and the like increase due to the incorporation of N, so that carriers excited by exposure and photo-discharge will be trapped into the gap states and then will be released from them by the electric field applied on a next charging process thereby removing the surface charges.
In addition, the plasma CVD method or sputtering method has been adopted to prepare the conventional a-SiC, a-SiN and a-SiO photoconductive films, which inevitably caused to yield a polymeric powder of (SiH.sub.2) on a film surface during deposition to thereby hinder a normal growth of film, and also needed a long time for the film formation due to low deposition rate thereof, to thereby remain a drawback for cost saving.
Besides, in the prior art, the a-SiC, a-SiO and a-SiN photoconductive films obstained do not possess sufficient photosensitivety to be used for electrophotographic photosensitive member and do not contain an H content of at least 40 atomic %.
A preparation method for amorphous silicon films utilizing the electron cyclotron resonance (ECR) method has been proposed (see U.S. Pat. No. 4,532,199).